Effect of soil properties on phosphate adsorption in calcareous soils ofPakistan
2002
Javid, S.,Ayub Agricultural Research Inst., Faisalabad (Pakistan). SoilChemistry Section
Adsorption isotherms were constructed to study the P dynamics incalcareous soils. For this purpose thirteen soil series from Pakistan andone from England were used. Adsorption isotherms were developed using 25ml of 10 mM CaCl2 solution containing a series of phosphate concentrations.The soils were equilibrated with phosphate by shaking the samples endover end for 24 h. The isotherms were examined by using Langmuir andFreundlich equations. The parameters of the equations were related to soilproperties. The adsorption data indicated that only one calcareous soilshowed precipitation when the final P concentration in the equilibriumsolution exceeded 26 mug ml-1. The adsorption data were well described byboth equations. In calcareous soils the plots of the Langmuir equation werecurvilinear rather than straight lines. The P adsorption capacities (Pmaxima and buffer power) were well correlated with clay and organicmatter contents of the soils (r2 0.75 and 0.81 for clay and 0.60 and 0.65for organic matter respectively). Phosphate adsorption capacities showedpoor correlation with total CaCO3 content (r2 0.16 and 0.29). This suggeststhat surface area of calcium carbonate in these soils is not simply relatedto total CaCO3. No other measured soil properties were correlated with Padsorption capacities.
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